Multi-story structures, such as office buildings and parking garages, are often built one story at a time from reinforced poured concrete. Such structures require numerous concrete pillars or columns for their structural support. In the case of square or rectangular cross section columns, many columns are constructed with a chamfer or bevel along the whole length of each vertical edge of the column.
To make high-rise buildings, it is imperative that each stack of columns be precisely aligned along a single vertical center line. Thus, when each story is poured, each column must be squared, that is, adjoining faces of the column walls must all meet at a 90.degree. angle throughout the length of the column and be plumbed. If the alignment of columns is off only slightly in each story, the cumulative effect of errors will result in a structure that is substantially weaker than its designers intended.
When a floor has been built and more stories will be added on top of it, carpenters using two-by-four timbers layout a full-sized template of supporting columns. The size of the template for a concrete column is just large enough to accommodate an assembled concrete form. The form itself, then, must be set up in a remote location, generally a handy open area twenty or more feet from the installation site. In work according to the prior art, to set up, pour, and strip the form from a finished eight foot concrete column normally requires approximately eight man hours of work per column at a cost of approximately $125 per column in labor. The problems encountered in pouring and finishing such columns to an acceptable level account for the large effort required.
Typically, forms for columns are assembled from form panels that are fastened together to form a mold panel. Such form panels typically include a frame of aluminum and a mold surface of high density plywood or high density overlay plywood, which has phenolic coating, which extends the life of the panel.
Chamfer strips of the prior art typically are wood or extruded plastic chamfer strips that are nailed to the plywood panels of the forms. The practice of using wood or plastic chamfer strips creates several problems. First, they are difficult to install, requiring at best about twenty minutes each to install. Their installation requires a man to be inside the form, which means at least one side of the form must be left open while one worker applies the chamfer strips along the inside edges of the form. Since the form is typically only large enough to allow one worker to enter it, other workers may be idle while the chamfer strips are being nailed on.
Second, when the plywood or high density overlay plywood is punctured, concrete, moisture, mold spores and so on find their way into the interior of the wood panel. When chamfer strips are repeatedly nailed to the plywood, a great many holes are formed in the plywood close to the metallic frame. These two processes dramatically reduce the useful life of the mold panel, which is expensive to replace.
Third, after the form is closed, squared, and moved into position on the floor template, one or more chamfer strips frequently come loose, requiring the column form to be removed from the template, reopened and fixed. Finally, the forces created by pouring concrete into the form frequently rip one or more chamfer strips from the form panel. These strips may disappear and become wholly-embedded in the column. A portion of the chamfer strip may break off and a portion of it may protrude from the finished column. Less dramatically, concrete frequently seeps between the edges of the column form panels and the chamfer strip. In all such cases, when the form panels are removed, the chamfer is either imperfectly formed or not formed at all. Building inspectors routinely insist that the chamfers on these columns meet the plan specifications, requiring substantial amount of work in grinding to put a chamfer on the finished column.
Not surprisingly, after such abuse, chamfer strips according to the prior art can be used only one to three times at a maximum before they must be discarded. In addition, extruded plastic chamfer material suffers from several disadvantages of its own. At the job site, it is typically stacked in a pile and each strip assumes whatever shape gravity dictates, so that each becomes deformed and cannot be straightened out, especially in cold weather. Forces bearing on them during form set up and concrete pouring also tend to distort them, by pushing them beyond their yield point.
Typically, the four mold panels of a prior art form system are held together by a simple corner flange approximately 90.degree., or angle iron disposed along each vertical edge of the panels and bolted thereto. Each form is individually squared, primarily by twisting the panels until all the diagonals of the open ends of the form are the same length and inserting loose shims or spacers between the corner flange and the mold panels, then tightening the bolts that hold the angle iron to the side rails while the form is in its remote location. Given the weight of the form panels themselves, and the forces exerted on them as the form is moved from the set up location to the pouring location, torsion frequently twists the column form so that it is out of square after being moved to the pouring site. In addition the shims frequently fall out during the moving of the form, and must be reinserted. The prior art corner strip does not effectively resist or adjust for these torsional forces and cannot maintain a 90.degree. angle between the wings.
Accordingly, there is a need for a system for forming a mold for a concrete column that reduces the high labor costs associated with pouring concrete columns; that reduces the difficulty of applying chamfer strips to the inside of the form; that provides a good square fit between the interior edges of the form panels and the legs of the chamfer strip; that provides a chamfer strip that will not come loose during pouring; that provides a chamfer strip that will not reduce the service life of the form panels; that eliminates extra labor costs involved in chamfering a column on which no chamfer was formed during the molding process; that provides chamfer strip having an extended or indefinite life; that provides chamfer strip that will not warp; that provides a form for a concrete column that can be easily squared and will remain square while the form is moved from the set up site to the pouring site; and that significantly strengthens the assembled form panels, thereby allowing lighter-weight form panels to be used in a given application.